Devices for retaining the sliding shoes of barrel pumps and motors

ABSTRACT

This device for retaining the hydrostatic shoes of oleohydraulic pumps or motors of the barrel-cylinder type comprises a bearing member formed with peripheral recesses which urges said shoes against an inclined plane surface in conjunction with the thrust exerted by a part-spherical washer responsive to a resilient member prestressed between a bearing face of the driving shaft and the part-spherical washer, the flexion of said resilient member being adjustable in a manner known per se by means of a device for adjusting the operating play between the hydrostatic shoes and the inclined plane surface.

Maistrelli 1451 Apr. 16, 1974 DEVICES FOR RETAININGYTHE SLIDING SHOES OFBARREL PUMPSAND MOTORS [75] Inventor: Roger-A. Maistrelli, Billancourt,

France [73] Assignee: Regie Nationale Des Usines Renault,

Billancourt, France [22] Filed: June 9, 1971 [21] Appl. No.: 151,450

[30] Foreign Application Priority Data 3,274,897 9/1966 Reinke 9l/507Primary Examiner-William L. Freeh Assistant Examiner- Gregory La PointeAttorney, Agent, or Firm-Stevens, Davis, Miller and Mosher [5 7 ABSTRACTThis device for retaining the hydrostatic shoes of elechydraulic pumpsor motors of the barrel-cylinder type July7, 1970 France ..70.25147Comprises a bearing member formed with Peripheral recesses which urgessaid shoes against an inclined [52] U.S. Cl. 91/488 Plans g inConjunction i the thrust exerteq by 1] Cl. a part phericalwasherresponsive to a resilient fnem- [58] held of Search 9 8 506 berprestressed betweena bearing face of the driving shaft and thepart-spherical washer, the flexion of 'said [56] References cuedresilient member being adjustable in a manner known UNITED STATESPATENTS per se by means of a device for adjusting the operating2,953,099 9/1960 Blibzich 91/507 P y between h hydrostatic Shoes and theinclined 3,292,553 12 1966 Hann 91/507 plane surface. 3,543,649 l2/l970Martin 91/507 3 l73,376 3/1965 Hulman et al. 91/488 2 C 9 F'gures1,710,567 4/1929 Carey 91/488 1 I 1 1 I I X/ A A I 3 t L rg x 25 7 i I,7 1:/ a e; h i 1 {Ag/y /V 5 4 1 10 a 9 DEVICES FOR RETAINING THE SLIDINGSHOES OF BARREL PUMPS AND MOTORS The present invention relates ingeneral to oleohydraulic pumps and motors of the barrel-cylinder type,wherein the pistons are reciprocated in a direction parallel to the axisof the pump or motor. This reciprocating motion is controlled by animpeller or swash plate on which the piston heads are caused to slide,these piston heads being generally provided to this end with socalledhydrostatic sliding shoes. 1

It is the essential object of the present invention to provide means forconstantly urging said shoes against said swash plate.

In the following disclosure only pumps will be referred to for the sakeof simplicity, but it will be readily understood by those conversantwith the art that this disclosure applies as well to motors of theaforesaid type.

During a rotation of the pump cylinder barrel, it is known that eachpiston is accelerated during the delivery stroke, then accelerated againbut in the reverse direction and also decelerated in this reversedirection during the suction phase. During the delivery strokedeceleration, and during the suction strokeacceleration,

the vis inertia or kinetic energy of the pistons and shoes tend toseprated these shoes from the swash plate. On the other hand, during thesuction stroke, the'friction force developing between the pistons andcylinders tends to facilitate this separation. Though the deliverypressure of the pump, during one fraction of the movement urges thepistons and shoes towards the plate, complementary retaining means are'provided so that their efiiciency can be relied upon under all operatingconditions.

Pumps are well known wherein the hydrostatic shoes are urged against theswash plate by a retaining plate. This retaining plate has formedtherein a recess for a dished washer urged by a spring tensioned orprestressed between the washer and the bottom of said re cess, so thatthis spring also assists in pressing the cylinder barrel against thedistributor plate.

This arrangement is attended by the exertion, by the cylinder barrel, ofan excessive pressure against the distributor plate, in comparison withthe force necessary for ensuring a satisfactory pump operation when thepump is of the high rotational speed type, for the kinetic energyexerted on the pistons are abnormally high. The considerable forceurging the barrel against distributor plate are particularly detrimentalwhen the pump is started.

Pumps are known wherein the sliding shoes crimped on the piston headsare constantly urged against the swash plate by a retaining-plate urgedin turn against the plate by tappets screwed to said plate. However,this arrangement is objectionable in that it requires a high degree ofprecision as far as the thicknesses of the retaining plate, of the shoebases and of the tappets are concerned, in order to avoid any excessiveplay or, in contrast thereto, any jamming of the parts involved. It alsorequires a good condition of ,the contact surfaces between the plate andtappets, for the relative speed between shoes and tappets may causepremature wear or sizing. v

In the French Pat. No. 1,577,889 there is described a pump wherein thepistons are crimped on the partspherical heads of the hydrostatic shoes.The shoes engage a rotary, hydrostatically balanced plate bearingagainst the swash plate. A shoe retaining plate is rigidly connected bymeans of screws to the rotary plate and prevents the shoes from movingaway from this rotary plate due to the provision of recesses slidablyengaged by the flat base faces of said shoes.

Now this arrangement requires an accurate machining of these base facesand also of the retaining recesses, if it is desired to eliminate anyrisk of seizing, without resorting to unduly broad machining tolerances.

On the other hand, the sum of the efforts due to the kinetic energy orvis inertia of the different pistons and shoes produces a torque tendingto increase the inclination of the retaining plate in relation to thebarrel axis. The corresponding reaction torque can be provided only byan eccentric reaction of the swash plate which is balanced by aprestressed spring housed in the barrel. The aforesaid spring musttherefore have dimensions sufficient to compensate this reaction in casethe pump were caused to rotate at high speed under zero load conditions.Since this spring also urges the barrel against the distributor plate,the sliding contact surfaces of the barrel and/or distributor plate aremost likely to be damaged when the pump is operated under theseconditions.

The device according to this invention is intended for retaining thepistons and sliding shoes of pumps and motors of the above-defined typeagainst the surface of the swash or impeller plate by means of aconnecting device of the type permitting the adjustment and taking up ofplay through aresilient member. This invention is also directed to anelastic coupling member adapted to exert on the shoes moderate retainingforces at low speeds and relatively considerable retaining forces athigh speeds.

Furthermore, this invention provides a shoe retaining device permittingthe separate adjustment of the force urging the cylinder barrel againstthe distributor plate.

The device according to this invention, which comprises a bearing memberformed with peripheral recesses and adapted to press the shoes againstan inclined flat surface in conjunction with the thrust exerted by apart-spherical washer responsive to the action of a resilient member, ischaracterized in that said resilient member is mounted in a prestressedcondition between a bearingsurface formed on the pump driving shaft andthe part-spherical washer, and that the permissible flexion of saidresilient member is adjustable in a manner known per se by means of adevice for adjusting the op- I crating clearance between the hydrostaticshoes and said inclined flat surface.

Other features and advantages of this arrangement willbe disclosed asthe following description proceeds ,with reference to the accompanyingdrawings illustrating diagrammatically by way of example a few typicalforms of embodiment of the invention.

In the drawings:

FIG. 1 is a sectional view of a pump, the section being taken along theline I'I of FIG. 2;

FIG. 2 is an end view of the pump barrel;

FIG. 3 is a fragmentary sectional view of the pump, taken along the lineIIIIII of FIG. 2;

FIG. 4 is a plane view of the pump shoes bearing member;

FIG. 5 is a section taken along the line VV of FIG. 4;-

FIG. 6 is an orthogonal projection on the impeller or swash plate of therotational axis of the cylinder barrel and of the path of the point ofintersection of the axis of rotation of the shoe on the plate surface;

FIG. 7 is a sectional view showing a hydrostatic shoe on a larger scale,and

FIGS. 8 and 9 are two axial sectional views showing two modified formsof embodiment of pumps according to this invention.

Referring to the drawings, the hydrostatic shoes 1 are connected to therelevant pistons 2 by means of partspherical ball members 3 retained bya circlip.

These hydrostatic shoes 1 are adapted to slide on the registeringsurface of a rotary plate 4 bearing in turn against the swash orimpeller plate 5. This plate 5 comprises hydraulic bearings 6corresponding in shape to the hydraulic bearings 7 provided between thecylinder barrel 8 and the distributor plate 9. A hearing member 10contacting the face 11 of said hydrostatic shoes 1 is formed withrecesses 12, shown more in detail in FIGS. 4 and 5, which permit thepassage of the cylindrical necks 13 of said shoes. The bearing member 10comprises on the other hand a recess 14 having a partspherical surfacecentered to the axis of rotation of plate 4 and at least two centeringstuds 15. This bearing member 10 is centered by means of itspart-spherical surface 14 engaging a washer 16 bounded by apartspherical outer surface complementary to the surface 14 of member10, and centered to the shaft 17 of the pump and in the plane of thecenters of the partspherical or ball members 3 of the hydrostatic shoes.The bearing member 10 engages one face of shaft 17 (shown in the form ofits spline l8 connecting this shaft to cylinder barrel 8) through themedium of a resilient member such as an elastic washer l9 and a rigidwasher 20. The elastic washer 19 is adapted, from its unstressedcondition, to be deflected by a few tenths of millimeter. The centeringand rotary coupling or rotary gaging the recesses 12 of this bearingmember with a play sufficient to permit their relative movement duringthe operation of the device. In fact, as shown in FIG. 6, the projectionon the swash plate 5 of the swivel ball of each shoe 1 describes duringthe operation of the device an ellipse e, at an angular speed on and anamplitude varying during the movement at a rotational speed mo of barrel2 which is assumed to be constant. The angular shift a between theprojections, on swash plate 5, of the centers of two successive shoes 1will also vary during a barrel revolution, so that the bearing plate 10of which the recesses 12 are disposed at spaced angular intervals alongits periphery is driven in succession by all the shoes 1 during onefraction of a revolution.

The synchronous rotation of pistons 2, shoes I, bearing member 10 androtary plate 4 is necessary for delivering lubricating oil underpressure to the bearings 6 of impeller or swash plate 5 through orifices21 formed in the rotary plate 4 and opening into the shallow cavityformed in the sliding contact surface of the base of each shoe 1.

The centering studs 15 may consist of insert pieces. The swash orimpeller plate 5, of which the rear face has the shape of a portion ofcylinder having its axis directed towards the center of thepart-spherical surface of washer 16, engages the complementarycylindrical surface of the end bearing of the pump casing or body.

The shaft 17 is mounted in this bearing by means of a compoundrolling-contact bearing 22 comprising axial and radial rollers. Themounting is obtained by using a nut 23 engaging a counter-plate 24.

When assembling the parts, the adjustment device comprising this nut 23is tightened home, so that the resilient washer 19 is fully compressedand the parts inserted between the spline 18 of shaft 17 and the nut 23are in successive direct engagement, i.e., without any play. Then thenut 23 is released by an angle such that its axial movement correspondsto the desired operating clearance for the aforesaid stacked parts, andthe lock washer 25 is eventually bent to fix the desired adjustmentposition.

This play is sufficient for absorbing such dimensional variations in thestacked parts as may result from temperature variations, speed and loadvariations (which alter the thickness of the oil films), and also fromgeometrical defects. 1

In the following disclosure it will be assumed that the force necessaryfor compressing home the resilient washer 19, although of moderatemagnitude, is greater than the force of spring 26 of which the onlyfunction is to keep the barrel in frictional contact with thedistributor plate. It may be noted that the reverse disposal may be usedas well.

In the case illustrated by way of example the operating clearanceresulting from the calculated release of nut 23 is taken up completelyby the resilient washer 19, and the dimensional variations occurringduring the pump operation in the parts stacked between the shaft splinel8 and nut 23 are compensated by this resilient washer 19. Since thisplay remains relatively moderate in comparison with the total chamber ofwasher 19 in its unstressed condition, this washer produces an effortapproximating that required for obtaining its maximum compression.

As the pump shaft speed increases and as a function of the angle ofinclination of swash plate 5, the inertia or kinetic energy of pistons 2and hydrostatic shoes 1 increases and is attended by a reaction exertedby the aforesaid bearing member 10 against the part-spherical washer.16.

This reaction is subordinate to the pump pressure for during onefraction of the shoe movement the thrust exerted by the oil on thepistons balances the inertia forces tending to move the shoes away fromthe rotary plate.

However, as long as this reaction remains inferior to the pressureexerted by the resilient washer, the camber of this washer remainunchanged. When this reaction is superior to said pressure, theresilient washer is gradually compressed and the hydrostatic shoes moveaway from the rotary plate by a value depending on their position butremaining relatively moderate, of the order of magnitude of theoperating clearance contemplated initially.

Under these conditions, it will be seen that the arrangement accordingto this invention permits of adjusting the maximum play between therotary plate and the hydrostatic shoes by properly releasing thepreviously tightened nut 23 as explained hereinabove.

Under these conditions it will be seen that it is particularlyadvantageous to utilize a resilient washer such that the minimum forcenecessary for compressing same completelybe inferior to the force withwhich the complete set of shoes I bear against the swash plate.

It will also be seen that at low speeds the pressure exerted by bearingmember on shoes 1, by these shoes 1 on the rotary plate 4 and by thisrotary plate 4 on swash plate 5, are low in comparison with the pressurevalues necessary for overcoming the inertia forces at high speeds andwith a greater inclination of swash plate 5. Therefore, the mechanicalefficiency at low speed is improved and the risks of seizing the partsare reduced considerably.

This arrangement further permits a proper choice of the spring 26 urgingthe barrel against the distributor plate, since the spring action isindependent of that of said resilient washer l9 urging the bearingmember 10, shoes 1 and rotary plate 4 against the swash plate 5.Consequently, these two resilient forces may be adjusted separately.

Another advantage resulting from this arrangement is that it minimizesthe degree of overhang of the radial effort exerted on piston heads inthe outermost position of these pistons in relation to their cylinders,this overhang being eliminated completely in the innermost position.

FIG. 7 illustrates another possibility of synchronizing and centeringthe rotary plate 4 in relation to the'hydrostatic shoes 1 by means ofstuds inserted in these shoes 1 and engaging corresponding recesses 27formed in the rotary plate, with a play sufficient for permitting theirrelative movements during the pump operation; in fact, any point of theaxis of each stud 15 describes an ellipse whereas the center of eachrecess 27 describes a circle as already explained hereinabove. The studs15 are hollow and comprise a slot 28 permitting the delivery of oil tothe shoe bearing and to the impeller or swash plate bearings 6.

It will be noted that these studs 15 may as well be secured to therotary plate 4, the operating play being provided in this case by arecess similar to recesses 27 but formed in the shoe.

Moreover, it is clear that the operating play adjustment nut 23may bereplaced by a circlip, the counterplate 24 being in this case selectedamong a series of gauged counterplates having different thicknesses, thechoice of the proper plate 24 being subordinate to the measurement ofthe necessary play when assembling the parts.

According to the modified form of embodiment illustrated in FIG. 8 thehydrostatic shoes -1 are in direct sliding contact with the swash plate5, without any intermediate rotary plate. On the other hand, nocentering studs are provided on the bearing member 10. This arrangementis advantageous in-that it is considerably simpler but attended by aconsiderable speed in the relative sliding movements between shoe andplate; thus, the thrust, not hydrostatically, is relatively highespecially when the angle of inclination of the swash plate isrelatively great. I

The arrangements described hereinabove are also applicable toconstant-output pumps. In this case the swash plate 5 is rigid with thepump body or casing.

They are also applicable to any type of swash or impeller plates,notably those adapted to pivot about pivot pins 30 of relatively smalldiameter, disposed on either side of the barrel and having their commonaxis disposed in the plate containing the centers of the partsphericalball members 3 of the hydrostatic shoes 1, this axis also passingthrough the center of the spherical surface of the part-spherical washer16, as illustrated in FIG. 9.

Although a few forms of embodiment of this invention have been describedand illustrated herein, it will readily occur to those conversant withthe art that various modifications and variations may be brought theretowithout departing from the spirit and scope of the invention as setforth in the appended claims.

What is claimed as new is: 1. Device for retaining the hydrostatic shoesof oleohydraulic pumps and motors of the barrel-cylinder type, whereinthe pistons are reciprocated by means of a swash plate inclined inrelation to the axis of rotation of the barrel in a direction parallelto the driving shaft of said pump or motor and the barrel-cylinder beingurged toward the distributor plate by a spring, this device comprising abearing member formed with peripheral recesses urging the shoes againstan inclined plane surface in conjunction with the thrust exerted by apartspherical washer responsive to the action of a resilient washer,said resilient washer being mounted in a prestressed condition between abearing face located on the driving shaft and said part-sphericalwasher, the flexion of said resilient washer being adjustable by meansof a device for adjusting the operation clearance between thehydrostatic shoes and said inclined plane surface comprising a meansexternal to the device and adapted to permit the axial positioning ofsaid driving shaft so that said resilient washer can yield at high speedand said inclined plane surface held in sliding contact with said shoesbeing formed on a rotary plate centered and rotatably driven togetherwith said bearing member by the mutual engagement of studs and recessestherefor, said rotary plate being provided with orifices permitting thepassage of fluid, the number of these orifices corresponding to that ofsaid shoes, said orificesopening under each shoe and also into ahydrostatic bearing provided between the rotary plate and said swashplate.

2. Device for retaining the hydrostatic shoes of oleohydraulic pumps andmotors of the barrel-cylinder type, wherein the pistons are reciprocatedby means of a swash plate inclined in relation to the axis of rotationof the barrel in a direction parallel to the driving shaft of said pumpor motor and the barrel-cylinder being urged toward the distributorplate by a spring, this device comprising a bearing member formed withperipheral recesses urging the shoes against an inclined plate surfacein conjunction with the thrust exerted by a partspherical washerresponsive to the action of a resilient washer, said resilient washerbeing mounted in a prestressed condition between a bearing face locatedon the driving shaft and said part-spherical washer, the flexion of saidresilient washer being adjustable by means of a device for adjusting theoperation clearance between the hydrostatic shoes and said inclinedplate surface comprising a means external to the device and adapted topermit the axial positioning of said driving shaft so that saidresilient washer can yield at high speed and said inclined plane surfacein sliding contact 3 ,80 3 ,9 8 5 7 8 with the shoes being a rotaryplate centered and rotatsaid passage orifices opening under each shoerespecably driven with the shoes by the mutual engagement tively andinto a hydrostatic bearing of said rotary plate of studs and recessestherefor, said rotary plate having engaging said swash plate. fluidpassage orifices equal in number to said shoes,

1. Device for retaining the hydrostatic shoes of oleohydraulic pumps andmotors of the barrel-cylinder type, wherein the pistons are reciprocatedby means of a swash plate inclined in relation to the axis of rotationof the barrel in a direction parallel to the driving shaft of said pumpor motor and the barrel-cylinder being urged toward the distributorplate by a spring, this device comprising a bearing member formed withperipheral recesses urging the shoes against an inclined plane surfacein conjunction with the thrust exerted by a part-spherical washerresponsive to the action of a resilient washer, said resilient washerbeing mounted in a prestressed condition between a bearing face locatedon the driving shaft and said part-spherical washer, the flexion of saidresilient washer being adjustable by means of a device for adjusting theoperation clearance between the hydrostatic shoes and said inclinedplane surface comprising a means external to the device and adapted topermit the axial positioning of said driving shaft so that saidresilient washer can yield at high speed and said inclined plane surfaceheld in sliding contact with said shoes being formed on a rotary platecentered and rotatably driven together with said bearing member by themutual engagement of studs and recesses therefor, said rotary platebeing provided with orifices permitting the passage of fluid, the numberof these orifices corresponding to that of said shoes, said orificesopening under each shoe and also into a hydrostatic bearing providedbetween the rotary plate and said swash plate.
 2. Device for retainingthe hydrostatic shoes of oleohydraulic pumps and motors of thebarrel-cylinder type, wherein the pistons are reciprocated by means of aswash plate inclined in relation to the axis of rotation of the barrelin a direction parallel to the driving shaft of said pump or motor andthe barrel-cylinder being urged toward the distributor plate by aspring, this device comprising a bearing member formed with peripheralrecesses urging the shoes against an inclined plate surface inconjunction with the thrust exerted by a part-spherical washerresponsive to the action of a resilient washer, said resilient washerbeing mounted in a prestressed condition between a bearing face locatedon the driving shaft and said part-spherical washer, the flexion of saidresilient washer being adjustable by means of a device for adjusting theoperation clearance between the hydrostatic shoes and said inclinedplate surface comprising a means external to the device and adapted topermit the axial positioning of said driving shaft so that saidresilient washer can yield at high speed and said inclined plane surfacein sliding contact with the shoes being a rotary plate centered androtatably driven with the shoes by the mutual engagement of studs andrecesses therefor, said rotary plate having fluid passage orifices equalin number to said shoes, said passage orifices opening under each shoerespectively and into a hydrostatic bearing of said rotary plateengaging said swash plate.